Two trans-4-aminoazoxybenzenes

Two isomeric trans-4-aminoazoxybenzenes, trans-1-(4-aminophenyl)-2-phenyldi azene 2-oxide (alpha, C12H11N3O) and trans-2-(4-aminophenyl)-1-phenyldiazen e 2-oxide (beta, C12H11N3O), have been characterized by X-ray diffraction. The alpha isomer is almost planar, having torsion angles along the C-aryl-N bonds of only 4.9 (2) and 8.0 (2)degrees. The relatively short C-aryl-N bo nd to the non-oxidized site of the azoxy group [1.401 (2) Angstrom], togeth er with the significant quinoid deformation of the respective phenyl ring, is evidence of conjugation between the aromatic sextet and the pi -electron system of the azoxy group. The geometry of the beta isomer is different. T he non-substituted phenyl ring is twisted with respect to the NNO plane by ca 50 degrees, whereas the substituted ring is almost coplanar with the NNO plane. The non-oxidized N atom in the beta isomer has increased sp(3) char acter, which leads to a decrease in the N-N-C bond angle to 116.8 (2)degree s, in contrast with 120.9 (1)degrees for the ff isomer. The deformation of the C-C-C angles (1-2 degrees) in the phenyl rings at the substitution posi tions is evidence of the different character of the oxidized and non-oxidiz ed N atoms of the azoxy group. In the crystal structures, molecules of both isomers are arranged in chains connected by weak N-H . . .O (alpha and bet a) and N-H . . .N (beta) hydrogen bonds.